Preliminary design of a reinforced concrete structure involves the selection and representation of a framing scheme, showing size and shape of beams, columns, and slabs. Preliminary design serves three purposes. First, it provides information to the owner, architect, mechanical engineer, and other members of the project design team. The second reason is efficiency. A preliminary structural design facilitates an efficient completion of architectural drawings and the mechanical design and drawings. The third reason is optimization. A completed preliminary design establishes the quantity and cost of all concrete and formwork.


In preparing the preliminary design, the engineer should keep a number of design objectives in mind. These can be stated briefly as follows: provide structural safety; meet functional requirements; maximize serviceability; minimize construction costs; reduce design costs; speed up the construction schedule; coordinate the structural frame with mechanical, electrical, and non-structural elements; and recognize personal preferences.


The first step in preparing a preliminary design is to find the typical bay or panel. The next step is to establish the minimum slab thickness to give the required fire rating or to allow embedment of conduit or under-floor electrical raceways. After selecting the slab thickness and typical bay, the engineer next sketches as many different framing schemes as possible. The next step is to design each scheme and estimate the construction costs.